Degradable articles and methods of using such articles as degradable bait

ABSTRACT

A degradable article comprising a polyurethane polymer gel or foam whose polymer structure contains hydrolytically unstable ester linkages and various additives. The article can be constructed so that some of the additives are released from the article at a sustained rate. In a preferred embodiment the additives are sensory stimulants for marine or aquatic organisms and the article is used as bait for those organisms.

FIELD OF THE INVENTION

The invention relates to articles which are capable of degrading in theenvironment surrounding the article, as well as capable of releasingadditives at a sustained rate into that environment. The invention alsorelates to the method of using those articles as degradable artificialbait for aquatic or marine organisms such as fish.

BACKGROUND OF THE INVENTION

Articles prepared from degradable materials are becoming increasinglyimportant in view of findings that certain materials, such as plastics,remain intact over long periods of time. In the environment, articlesmade from materials that do not degrade sufficiently are havingconspicuously harmful and deleterious effects. For the ocean environmentin particular, it has been recently noted that even small, virtuallynon-degradable articles such as plastic artificial fishing worms used tobait a recreational fisherman's hooks have been found intact in theoceans and digestive tracts of marine mammals. Given artificial bait'spopularity among recreational fishermen, and as discussed below, giventhe commercial fishermen's increasing need for artificial baits, adegradable version of the article would be strongly desirable.

Artificial fishing bait has become especially popular with all types offishermen. For instance, recreational fishermen find this type of baitattractive because it is easy to store in a tackle box and it avoids thesometimes distasteful chore of handling and using natural bait such asworms or squid. However, recreational fishing represents just a smallportion of fishing activity. Commercial fishing activity represents thelarger portion of the fishing market and could benefit from anartificial bait in various ways.

For instance, artificial bait could be stored for long fishingexpeditions without worrying about the refrigeration normally requiredfor natural bait. The bait, which can be delivered in dry form, weighsmuch less than natural bait. It is anticipated that a ton of naturalbait can be replaced by a couple hundred pounds of the degradable bait.Similar savings on volume are also possible. In addition, if made insheet form, the bait could be delivered to and stored in commercialfishing vessels in rolls, for ease of handling. Even further, with theadvent of automatic baiting for commercial longline fishing vessels,such rolls can be more safely incorporated into a baiting procedure sothat the bait is cut and attached to hooks as the bait sheet unwindsfrom the roll.

Using this type of bait would be likely to reduce accidents whichsometimes occur when using automatic baiting of natural bait.Specifically, natural bait does not always have a uniform size nor is italways in a shape that is easily hooked. As a result, using natural baitrequires that someone continuously feed the bait operation and manuallyplace the bait in the slicer of the automatic baiter. This activitysometimes leads to the accidental cutting or hooking of hands orfingers. On the other hand, sheets of artificial bait can be cut to auniform size and fed to the hooks of the baiting equipment in a mannersuch that little manual handling is required.

Moreover, artificial bait can be more durable. Natural bait begins tolose its integrity after a period of time in the water and bait can belost by falling off the hook, or by sea gulls and small fish tearing thebait off the hook. If designed properly, artificial bait can remain onthe line for logger periods of time and made strong enough so that it isnot easily removed by tearing. In the end, such durability will likelyresult in larger catch yields.

However, as has been shown, the drawback to the artificial baits on themarket today is that they do not possess sufficient degradability. Forinstance, various bait constructions presently use poly(vinyl chloride),lead jigs and other plastic materials. All of these are believed to beessentially non-degradable materials. See U.S. Pat. Nos. 4,731,247issued to Wolford et al., Mar. 15, 1988 (cellulose ether andplasticizers); 4,666,717 issued to Smith et al., May 19, 1987(polyamines and copolymers of ethylene and ethylenically unsaturatedmonomers); 3,684,519 issued to Combs, Aug. 15, 1972 (polyacrylamide andmonomers); and PCT Application 87/07476 (polyurethane foams). As anexample, artificial baits such as the well-known plastic worms areprepared from poly(vinyl chloride) and have been known to remain intactfor many years. As recently reported, such plastic worms are being foundin the digestive tracts of sea otters. Thus, the harmful effects ofusing such articles are just beginning to manifest themselves, and ifcommercial fishermen are forced to look for alternatives to naturalbait, a degradable artificial alternative would certainly be desired.Likewise, other industries and markets would benefit from degradablearticles.

Various degradable materials which might be adapted for use as adegradable bait are known. For example, U.S. Pat. No. 4,132,839, issuedto Moran et al. Jan. 2, 1979, discloses prepolymers which, when foamed,provide biodegradable hydrophilic polyurethane foams. The question ofhow or whether such foams might be incorporated in a degradable baitwhich is palatable to fish and with sustained release capabilities isnot addressed. A bait which can release an attractant in a controlledmanner has been proposed in U.S. Pat. No. 4,245,520, issued to Carr Jan.20, 1981. Its formulation produced a gel which must be refrigerated orfrozen. U.S. Pat. No. 4,463,018, issued to Carr Jul. 31, 1984, usedgelatin, agar, locust bean gum, partially hydrolyzed cellulose, sorbicacid, and humectants such as glycerol, thus producing a material havingimproved heat stability and shelf life at the expense of palatability tofish.

Another reference, U.S. Pat. No. 3,410,689, issued to Nathan Nov. 12,1968, discloses a polyurethane foam mixed with an attractant as a baitwhich "disjoins," or breaks into relatively large pieces upon immersionin water. This bait relies on the break-up of the article to distributethe attractant.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a novel degradable, yetdurable, article which sufficiently degrades over an environmentallyacceptable period of time, wherein the article comprises a degradablepolyurethane polymer foam or gel and wherein the polymer hashydrolytically labile ester linkages.

It is also an object to provide a degradable article comprisingfunctional additives in an amount sufficient to be released from thearticle at a sustained rate.

It is also an object to provide a novel degradable bait for aquatic ormarine organisms wherein the bait comprises

(a) at least one layer of a degradable polyurethane polymer where thepolymer has hydrolytically labile ester linkages and

(b) sensory stimulant additives which are releasable from the bait at asustained rate sufficient to attract aquatic or marine organisms.

It is also an object to provide a novel method of attracting aquatic ormarine organisms wherein the method comprises using the degradable baitdescribed above.

Those of ordinary skill in the art would recognize that sensorystimulant additives might function as repellents as well as attractants.Such persons would also appreciate that the articles described hereinand their method of manufacture can be varied by methods known to thosewith skill in the art. Thus the invention is limited only by the claims,and is not to be confined to the embodiments and examples disclosed inthis application.

Furthermore, although this invention is conveniently described in termsof bait for fish, it should be noted that an article which is shown tobe degradable in water need not be used in water. For example, thearticle may be used as an insect attractant or repellant in air andthen, perhaps, disposed of in a landfill. Also, other aggressiveenvironments such as compost piles, activated sewage sludge, or thosecontaining detergent enzymes, extremes of pH or living tissues arecontemplated as being suitable to degrade the article.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section of a preferred embodiment of a degradablebait for aquatic or marine organisms. FIGS. 2 and 3 show the percentageof additive release over time from different preferred embodiments ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention uses polyurethane foam and gel fabricationtechnology to assemble one or more layers of polyurethane, reinforcingscrim, and adhesives or coatings into sheets, shapes or rolls withcharacteristics controlled for proper release of sensory stimulants. Thestimulants are introduced either during the curing operation or afterthe polyurethane has been cured. The polyurethane material is formulatedso that it will be storage stable when dry and, preferably, will swellwhen wet into a flesh-like consistency that has adequate strength for upto about three days, but which will degrade nd disappear after prolongedexposure to water, preferably within one year or less. In one of thepreferred embodiments, a degradable isocyanate-capped prepolymer havinglactate moieties present for easy enzymolysis and hydrolysis, is formedoptionally into a thin sheet, using an approximately equal amount of anaqueous solution of surfactant, such as a silicone surfactant, that willgive a relatively hydrophobic foam. The sheet is cast onto a movingbelt, and a strength reinforcing paper or scrim such as cheesecloth maybe laid down at the same time so that the scrim becomes positioned nearthe center of the sheet. The sheet is then immersed in a solution ofattractants; e.g., a mixture of selected amino acids, either with orwithout drying of the sheet between casting and impregnation. In thisoperation, because of the hydrophobic nature of the surfactant, it ispreferable to compress the sheet as it enters the attractant solution inorder to express air bubbles and to allow saturation. The reason for theuse of the hydrophobic surfactant is that it will be difficult to rewetthe bait sheet during use, thus prolonging the release of thewater-soluble chemosensory attractants. When this procedure is used toprepare sheets which are approximately 15% by weight of attractants, therate of release upon rewetting is such that about half of the attractantmaterial is released within one to eight hours, depending on the amountof agitation.

The degradability of the novel article depends on the presence ofhydrolytically labile ester linkages in the polyurethane foam. Thoselinkages can be introduced to the polymer structure of the foam by usinga polyol which has been reacted with an α-hydroxy carboxylic acid. Thepolyol can be used in well-known "one shot" and "prepolymer" methods forpreparing foams.

Generally, an α-hydroxy carboxylic acid is heated under reflux with apolyol. The acid and hydroxyl groups condense to form the desiredhydrolytically labile ester linkages. Optionally, the resultinghydroxyester polyol is mixed with another polyether or polyol. Thepolyol or polyol blend is usually dewatered in order to eliminatepossible side reactions in the subsequent steps. In the "one-shot"method, the polyol or polyol blend is mixed with an isocyanate, nearstoichiometric amounts of water, catalysts, and possibly otheradditives, and foams immediately. In the "prepolymer" method the polyolor polyol blend is capped with an isocyanate. The isocyanate-cappedhydroxyester polyether polyol, or prepolymer, will foam upon theaddition of water.

As used herein "degradability" of the article in an environment, meansthe ease of or the article's susceptibility to losing its physicalintegrity, i.e., breaking down into small particle form. For instance,in terms of an article used in a marine or aquatic environment,degradability means the ease of or susceptibility to losing its physicalintegrity over time under the conditions found in such environments,e.g., saline environment. It is also postulated that to achieve ultimatedegradability, the particles resulting from the breakdown describedabove should be susceptible to further decomposition wherein theparticles are consumed by ubiquitous environmental microbial agents.

Another aspect of degradability as it applies to baits is its effect onthe target organisms. If an item is degradable, there is the potentialfor the item to change too much in character, or to release materialswhich interfere with the action of the sensory stimulants included inthe bait. The degradable article would ideally be composed of a neutralcarrier with reasonably durable physical characteristics, which allowsthe sensory stimulants to be released, and then degrades withoutcounteracting its original purpose.

The hydroxy carboxylic acid, which is used to impart degradability tothe article, need not be the sole carboxylic acid used to react with thepolyol. Other acids, such as adipic acid, may be mixed with the hydroxycarboxylic acid to produce a degradable article. The use of a mixed-acidcomponent will affect the ultimate physical characteristics of thearticle, including its rate of degradation.

Suitable α-hydroxy carboxylic acids used to react with the polyol andimpart degradability are, preferably, lactic and glycolic acids. Theseare more preferred because they are very labile, and also cheap andreadily available. Other higher molecular weight α-hydroxy acids such asthe propionic, butyric, and isobutyric homologs are usable in thisinvention. The higher molecular weight acids have a lower reactivityduring polymer synthesis. If a higher molecular weight acid is used,some sort of catalyst or accelerator might be used during theesterification step.

The polyols used to react with the aliphatic hydroxy carboxylic acid arefrom one of two polyol systems. The two systems are (1) low molecularweight aliphatic or substituted aliphatic alcohols containing from 2 to8 hydroxyl groups per molecule, and (2) polyether or polyester polymericpolyols, or a mixture of the systems. Using a mixture of various polyolsmay be advisable to adjust the final article characteristics such asrate of degradation, texture, density and rate of release of theattractant and wettability of the article.

Suitable low molecular weight alcohols of the first polyol system have 2to 8 hydroxyl groups and a molecular weight of less than about 1000 andpreferably 500 or less. Specific alcohols include, but are not limitedto, butanediol, hexanediol, glycerol, 1,2,3-butanetriol,1,2,4-butanetriol, trimethylolethane, trimethylolpropane, erythritol,pentaerythritol, adonitol, arabitol, mannitol, sorbitol, iditol,dulcitol, sucrose, dipentaerythritol, triethanolamine and condensationproducts of ethylene and propylene oxides with ethylene diamine,diethylene triamine; and triethylene tetramine.

The polyether polyols of the second system preferably are essentiallylinear, have a molecular weight not exceeding about 4000, and mostpreferably not exceeding about 2000. Suitable polyethers are prepared byhomopolymerization of ethylene oxide, or propylene oxide, and includerandom copolymers and block copolymers such as polyoxyethylene diolcapped with polyoxypropylene chains and polyoxypropylene diols cappedwith polyoxyethylene. Suitable linear polyethers may also be prepared bycondensing an alkylene oxide of 4 carbons or less (e.g., ethylene,propylene or tetramethylene oxide) with a low molecular weightpolyhydroxylic alcohol such as those described above. In suchcondensation products the polyether chains are essentially linear andhave an average molecular weight of from 50 up to about 4000.Commercially available polyether polyols include CARBOWAX 600, 1000 and1450 (from Union Carbide Chemicals and Plastics Co., Danbury, Conn.).

Suitable linear polyester polymeric diols include those such as theFormrez 66 series (1,6-hexanediol adipates of molecular weight 500-3000)or the Formrez-II series (Diethylene glycol adipates of molecular weight500-3000) (supplied by Witco Chemical Corporation, New York, N.Y.).

Useful polyester and polyether polymeric triols include those having amolecular weight of about 1000 to 10,000, preferably 3,000-7,000.Commercially available polyether polyols include, for example, TPEG 990,an ethylene oxide-based triol having a nominal molecular weight of 990(from Union Carbide).

The hydroxy ester resulting from the mixture of the α-carboxylic acidand the polyols may be further combined with any of the above listedpolyols or a mixture thereof. The further addition of the polyols may beused to fine-tune degradability and other desirable traits of the finalarticle.

The polyol and the hydroxy acids are reacted together under conditionswell known for preparing such condensation products. See U.S. Pat. No.4,049,592 issued to Marans et al. Sep. 20, 1977. The followingillustrates several ways the polyol systems can be used to prepare thecondensation products containing the labile ester linkages.

A. A low molecular weight alcohol and sufficient hydroxyacid arecombined to form a condensation reaction product. The hydroxy acidshould be reacted with the alcohol in amounts sufficient to completelyesterify. The preferably trifunctional, hydroxyacid ester condensationproduct serves as a crosslinking agent for a linear polyether polyol(e.g., polyoxyethylene glycol) system by providing branching units. Inaddition, it imparts degradability to the foam which ultimately results.The hydroxy acid ester is also employed in amounts sufficient to providethe desired properties, i.e., if it is desired to increase rigidity,solvent resistance and other properties associated with crosslinkdensity, the amount of crosslinking agent is increased.

B. Linear polyether and polyester polyols completely esterified withhydroxy acid (preferably lactic acid) and blended with the low molecularweight alcohol can be used.

C. A polyester or polyether polymeric triol condensed with an α-hydroxyacid, may be used.

D. The hydroxy acid ester condensation product formed in A above can becondensed with ethylene or propylene oxides to form essentially linearpolyether chains originating with the hydroxy groups of the ester. Suchchains would have the molecular weight distribution as described abovefor the linear and triol polyethers. This system may be exemplified bythe trimethylolpropane (or ethane) ester formed by condensation withlactic acid followed by further condensation of the hydroxyl groups ofthe ester (3 per mole) with ethylene oxide to provide polyols havingthree essentially linear polyether chains per mole.

As mentioned above, the polyols (or polyol blend) are next capped with apolyisocyanate to make a liquid prepolymer.

The polyisocyanates suitable for capping the polyols includepolyisocyanates such as the polyaryl polyisocyanate described in U.S.Pat. No. 2,683,730, toluene diisocyanate ("TDI"),triphenylmethane-4,4',4",-triisocyanate, benzene-1,3,5-triisocyanate,hexamethylene diisocyanate, xylene diisocyanate, isophoronediisocyanate, chlorophenylene diisocyanate,diphenylmethane-4,4'-diisocyanate, naphthalene-1,5-diisocyanate,xylene-alpha, 3,3'-dimethyl-4,4'-biphenylene diisocyanate,2,2',5,5'-tetramethyl-4,4'-biphenylene diisocyanate, 4,4'-methylenebis(phenylisocyanate), 4,4'-sulfonylbis (phenylisocyanate), ethylenediisocyanate, trimethylene-diisocyanate and the like. TDI is mostpreferable. Mixtures of any one or more of the above-mentioned organicisocyanates may be used as desired. The polyisocyanates or mixturesthereof which are especially suitable are those which are commerciallyavailable, have a high degree of reactivity and a relatively low cost,e.g., TDI. Thus, the aromatic isocyanates are preferred. However, ifgreater hydrolytic and color retention stability are desired, aliphaticand cycloaliphatic diisocyanates are preferred.

Capping is preferably effected by using an excess of isocyanate toinsure complete capping of the polyol. Thus, the ratio of isocyanategroups to the hydroxyl groups used for capping is between about 1.8 toabout 4 isocyanate to hydroxyl, and preferably about 2.1 to about 3isocyanate to hydroxyl molar ratio. In order to achieve a crosslinkednetwork formation on foaming, the reactive components may be formulatedin a variety of ways. For example, when water is the sole reactant withthe isocyanate groups leading to chain growth during the foamingprocess, the isocyanate-capped reaction product preferably has anaverage isocyanate functionality from about 2 and up to about 6 or moredepending upon the composition of the polyol and capping agentcomponents. When the isocyanate capped reaction product has anisocyanate functionality of only about two, then the aqueous reactantmay contain a dissolved or dispersed isocyanate-reactive crosslinkingagent having an effective functionality greater than two. In this case,the reactive crosslinking agent is reacted with the capped resin whenadmixed during and after the foaming process has been initiated. Whenthe isocyanate capped resin has an isocyanate functionality of onlyabout two, then a polyisocyanate crosslinking agent having an isocyanatefunctionality great than two may be incorporated therein, eitherpreformed or formed in situ, and the resultant mixture may then bereacted with the aqueous reactant, optionally containing dissolved ordispersed isocyanate-reactive crosslinking agent leading to acrosslinked, infinite network hydrophilic polyurethane foam.

As indicated above, when the first linear polyol containing system isused, a crosslinking agent is preferably used. Those agents not onlyinclude the low molecular weight alcohols which have been reacted withthe hydroxy acid, but also include the unreacted low molecular weightalcohols as well as other water soluble or water dispersiblecrosslinking agents can be used. The agents should be polyfunctional andreactive with isocyanate groups. Agents other than the low molecularweight alcohols listed earlier include, but are not limited to,materials such as diethylenetriamine, triethylenetetramine,tetraethylenepentamine, polyethyleneimine, toluene-2,4,6-triamine,ethylenediamine, aminoethanol, trimethylenediamine,tetramethylenediamine, pentamethylenediamine, hexamethylenediamine,ethanolamine, diethanolamine, hydrazine, benzene-1,2,4-tricarboxylicacid, nitrilotriacetic acid, citric acid, 4,4'-methylenebis(o-chloroaniline), and the like. The water soluble or water dispersiblecrosslinking agents chosen are those which cause a crosslinked networkto form during or after the foaming process begins to take place. Whenusing the triol containing polyol system, or some linear diol systems, acrosslinking agent may not be required.

In the alternative a diol-based material or a mixture having an overallfunctionality of about two or less can be converted into a suitablystrong foam material by heating with excess isocyanate sufficient toallow formation of allophanates or other by-products of the isocyanatereaction.

The Aqueous Component

To effect foaming and preparation of the crosslinked degradable polymernetwork, the component including the hydroxyester polyol or polyol blendis simply combined with an aqueous component.

When water is added to the polymer in either the one-shot or prepolymermethod, other ingredients may be included with the water. Potentialadditives include catalysts and surfactants or cell structure controlagents which regulate the size, density, and degree of openness of thefoam cell structure. That is, they control such properties as texture,slipperiness and density of the final article. Such commerciallyavailable surfactants include as Hamposyl-O®, (an oleate sarcosine (fromW. R. Grace & Co.-Conn., Lexington, Mass.), Brij 72® (from ICI Americas,Bloomington, Del.) and others known to those of ordinary skill in theart. Further additives may be used to control the surface texture or"feel." For example Polyox®, a high molecular weight (5-10 million)polyethylene glycol (from Union Carbide), may be used to impart aslippery feel. Similar results may be obtained with Carbopol, apolyacrylic acid polymer (from Union Carbide). Generally, pigments, dyesand colorants, as well as anti-mold agents such as polysorbates, may beadded at this stage.

Control of foam structure is one convenient method to control the rateof release of the sensory attractants. It has been observed that a foamhaving small cells that have a multiplicity of cell windows in place(i.e., a high content of partly closed cells) releases a stimulant moreslowly than a foam having an open cell, largely reticulated structure.

The way in which addition of water influences the foams obtained can beillustrated by the following water index value: ##EQU1## Thus, becauseone-half mole of water is equal to one equivalent of isocyanate, where0.5 mole H₂ O is used with 1 eq. NCO, the water index value is 100.

An index of 100 indicates that both equivalents are equal or "balanced".An Index of 95 indicates that there is a 5% deficiency of water. Aslight theoretical excess of isocyanate, usually 3-5%, is commonpractice in the prior art, particularly with flexible foams made by theone-shot method mentioned above and described in more detail below.

Using the prepolymer method and water in amounts from about H₂ O IndexValue of 100 up to about H₂ O Index Value of 200, poor foaming resultsunless materials such as surfactants or the like are included. Amountsup to about H₂ O Index Value of 200 require a catalyst. When using a H₂O Index Value of about 78,000, surprisingly good foams result whichimprove in characteristics with added amounts of molar water. Thus, theavailable water content in the aqueous reactant is from about an H₂ OIndex Value of about 1300 to about 78,000 and desirably from about 4,000to about 40,000.

"Available water" in the aqueous reactant is that water accessible forreaction with the prepolymer, and which is exclusive of water which mayform a layer during reaction, or supplemental water which may benecessary because of additives present in the forming the aqueousreactant.

Because large amounts of water are in the aqueous reactant duringreaction, i.e., the present system is not dependent upon a molarNCO-water type reaction, it is possible to combine a great variety ofmaterials in the aqueous reactant which are otherwise not possible withlimited water reacting systems.

The aqueous reactant may be used at temperatures from about 2° C. toabout 100° C. as desired.

Although the prepolymer is easily foamed by the above process, it isalso possible to add, although not necessary, supplemental foamingmaterials such as those well known to the artificial sponge foaming art.

After foaming has been effected, the foam may be dried, if desired,under vacuum from 1 to 760 Torr at a temperature of about 0° to about150° C. If the foams are to be in sterile environments, the foams may beheat or chemically sterilized prior to use.

An alternative to the prepolymer method described above is thewell-known "one shot" method of preparing a polyurethane foam. Insteadof reacting the hydroxyester polyol or polyol blends with theisocyanates prior to the addition of water, the polyols, isocyanates,and water are reacted simultaneously. When using the one shot method,catalysts such as tin salts, iron salts or the like are required topromote the chain extension reaction of the polyols' hydroxyl groups.Other catalysts, such as tertiary amines, are used to promote theevolution of CO₂ as a result of the reaction of water and isocyanates.

Although this invention is described in terms of producing a foamedarticle, non-foamed articles can be produced and are within the scope ofthe invention. A foamed article is produced when (1) the hydroxyesterpolyol or polyol blend is mixed with isocyanate and water or (2) theisocyanate capped hydroxyester polyol or polyol blend is mixed withwater. The hydroxyl groups from the water and the isocyanate groupsreact with the evolution of CO₂ and consequent foaming. If polyamines,low molecular weight alcohols or polyols and the like are substitutedfor the water, CO₂ does not evolve, and foaming does not occur. Theproduct is an elastomeric gel instead of a foam.

Sensory Stimulant Additives

The additives which can be used in the degradable articles are variedand depend upon the article being made and the intended use of thearticle. The additives used herein should be releasable at a sustainedrate from the article. By "sustained rate," it is meant that the sensorystimulant additive is released gradually from the article over a periodof time. Control of foam structure and the method used to incorporatethe sensory stimulant into the article as well as the physical locationof the stimulant in the article are ways to control the rate of sensorystimulant release. For example, a foam structure having a large relativenumber of small, closed cells would tend to exhibit a slower releaserate. Similarly, a more hydrophobic foam would tend to release thesensory stimulants more slowly, as would a foam in which the sensorystimulant had been incorporated as part of the foam structure itself.Other additives incorporated in the foam may affect the release rate, aswell. The type of surfactant used, if any, may play an important role inrate of attractant release. In this context, nontoxic and biodegradablesurfactants would be especially preferred. Surfactants which may beconsidered as examples in this connection are HAMPOSYL® 0 and HAMPOSYL®1-30 (from W. R. Grace & Co.-Conn.; TRITON® CG-110 SURFACTANT (from Rohmand Haas Company, Philadelphia, Pa.); DOW CORNING® 190 SURFACTANT (fromDow Corning Corp., Midland, Mich.); SANDOTERIC® TFL and SANDOPAN® DTCLinear Gel (from Sandoz Chemicals Corp, Charlotte, N.C.), PLURONIC®F-87, F-108, and F-127 PRILL® and PLURONIC® L62 (from BASF CorporationChemicals Division, Parsipanny, N.J.). The additives could beincorporated within the interior of the foam or some other structure ofthe article, thus resulting in a prolonged sustained release of theadditives. On the other hand, the additives can be coated on the surfaceof the foam or the surfaces of other structures of the article. Thiswould likely result in a quick sustained release. The thickness of thearticle itself affects the release of the additives, with thickerarticles usually exhibiting a slower release of additives.

The additives can be incorporated by immersing the foam in a solution ofadditive components and allowing the foam to imbibe the additives.Another method includes adding the additives in the aqueous componentused in the above-mentioned polyurethane foaming methods. Thus, when thecrosslinked foam structure is formed, the additives become encapsulatedwithin the structure's interstices. This method would be especiallypreferable when the additives are in water insoluble form. In apreferred method, the additives are incorporated between layers ofdegradable foam.

Degradable Fish Bait

As described above, one use of the degradable article is in the field ofartificial bait for fish and other marine organisms. This embodiment ofthe degradable article uses the polyurethane foam and/or gel fabricationtechnology described above and comprises at least one layer of thedegradable polyurethane polymers described earlier. The bait alsocomprises sensory stimulant additives which are present in an amount andwhich are releasable from the bait at a sustained rate sufficient toattract the fish or other aquatic or marine organisms and incite them toingest the bait article.

One preferred structure of the bait employs a "sandwich" structure ofpreferably two additive-containing degradable foam layers which areadhered together by a degradable polymer adhesive. The process forconstructing the bait is described below in terms of making thesandwich-type embodiment, but the process employs well-knownfoam-forming and foam lamination techniques which can be easily modifiedto fabricate other constructions as well.

For instance, a prepolymer containing the hydrolytically labile esterlinkages described earlier and an aqueous component are reacted to forma thin sheet of polyurethane foam which is cast onto a release surfaceor a moving belt. Optionally, the foam is cast in the shape of a largebun or log, and then sliced with a saw or hot wire, etc., into sheetform. The sheet is then optionally dried before being immersed in asolution of sensory stimulant additives. To maximize the absorption anddistribution of additives, it may be preferable to compress the foamsheets before or after they enter the additive solution in order toexpress air bubbles.

Preferably, two unimbibed foam sheets are then laminated and adheredtogether preferably by a degradable polymer adhesive, and preferably anadhesive prepared from the same degradable polyurethane polymer used tomake the foam and the desired sensory stimulants described below.Well-known adhesive formulation techniques may be used to form a pastefrom the polymer and stimulants. The resulting paste is then applied toone or both layers of the degradable foam. The adhesive is then curedusing water (liquid or vapor) or other well known isocyanate reactivecuring agents, including polyols, polyamines and the like. Optionally,the resulting laminate can be further coated with a degradable material,which is also preferably a material comprising the same degradablepolymers. FIG. 1 illustrates a cross section of the sandwich-typestructure with 1 and 2 representing the two polyurethane layers and 3representing the adhesive.

With most baits, it will be preferable to construct the bait so that thethickness of the bait as a whole is in the range of 0.2 cm to 1.0 cm.However, other size baits might be required for certain species ofaquatic animals.

As discussed below, the thickness is not limited to a particular rangeand will depend on the release rate as well as the shape and texture ofbait desired. Likewise, the thickness of the adhesive layer can vary andwill depend on the same factors. As discussed below, sensory stimulantadditives may also be added to the adhesive layer and will affect thethickness of that layer.

In addition to having the adhesive layer and two foam layers, the abovesandwich construction can also have an additional layer forreinforcement of the bait structure. Such a layer enhances the strengthof the bait structure and facilitates the retention of the bait on abait hook. The layer would be especially preferable when used to baithooks on an automatic baiter. When used, the reinforcement layer ispreferably placed in between the two foam layers and laminated oradhered thereto. In an alternative embodiment, the reinforcing layer isplaced in the foam forming mixture during foaming so that when the foamforms, it forms around the reinforcing layer, thus encapsulating thelayer. The reinforcing layer may be varied in terms of coarseness andtype of material used in order to achieve the degree of strengthdesired. The reinforcing layer is preferably a degradable material suchas cheesecloth, tobacco cloth, paper, cellulosic wovens or non-wovens,or rayon.

It should be appreciated that because foams and gels can be easilymolded, the degradable bait can be in forms other than sandwich-typesheet described above. Using the appropriate molds, reinforcing layersand other additives, the construction can be in the form and color ofnatural bait such as frogs, minnows, worms or the like.

The sensory stimulant additives or attractants in the baits can be thosewell-known in the art. The additives can be olfactory and gustatorystimulants such as liquified or powdered fish or other marine products,fish oils, anise, amino acids or known synthetic liquid or solidattractants.

Additives which are in solid form include comminuted squid, shrimp,bunker or waste fish or parts normally disposed of during fishprocessing operations, e.g., fish heads, carcasses, etc. See U.S. Pat.No. 4,731,247 to Woolford et al.

In addition, additives can be prepared following the procedure ordisclosure in Ed. Hara, Chemoreception in Fishes, Elsivier ScientificPublishing Co., New York (1982).

The additives must be present in the bait in an amount and must bereleased at a sustained rate sufficient to attract the species desired.As used herein "sustained rate" means the gradual release into thetarget organism's environment over a period of time. An additive is"gradually released" when it takes longer to release from the articlethan if it were simply dumped into the environment. See U.S. Pat. No.4,731,247 to Woolford et al. The amounts and rates vary for the myriadof species, for some of which exemplary rates are described below.

For sport or recreational fishing for species such as bluefish,rockfish, etc., the release period is rather short, e.g., 15 minutes totwo hours; and the bait should be designed to effectively release theadditives over that time period. To achieve such release rates, thefollowing features of the bait should be considered:

(1) additives imbibed at the surface of the bait article,

(2) large amount of additives,

(3) when additives are imbibed in one of the foam layers, the foamshould be open-celled and preferably free of skin layer and cut in thinlayers, and

(4) use of coatings and impregnants, instead of the foam, for therelease site of the additives, and

(5) use of foams with an open pore structure.

In commercial fishing for species such as haddock, salmon, cod, torskand tuna, the release period should be longer, e.g., over 1 to 20 hourperiod or longer. For lobster baits, the release period shouldpreferably be from 3 to 5 days. To achieve those periods of release, thefollowing features of the bait should be considered:

(1) thorough saturation of the bait article with additives,

(2) encapsulated solid or liquid additives, e.g., comminuted fish scrapsand oils;

(3) adhesive layer which contains attractant additives,

(4) foam density or heavy skin layers,

(5) when the foam layers are imbibed with additives, use of thick foamlayers, and

(6) a more closed pore structure.

As mentioned above, using the above-described article as an artificialbait for fish is just one embodiment of the degradable article, andother uses can be envisioned as well. Degradable articles with thecapability of sustained release of additives would be useful forsurgical implants and pharmaceuticals, wound dressings and medicaments,personal care items such as diapers and the like. To accommodate each ofthe above uses, the release of the additives would be controlled anddesigned in a similar fashion to the controlled release of the sensorystimulating additives of the fish bait. For some applications, theadditives may be contained in particles, or other defined shapes, asopposed to layers.

The following examples are provided to illustrate the invention andshould not be interpreted as limiting the scope thereof or the claimswhich follow the examples.

I PREPOLYMERS Example 1

A mixture of 336.8 g (2.5 moles) of trimethylolpropane and 1399 g (13.7moles) of 88% lactic acid were heated under reflux for six hours at 115°C., then 15 hours at 135° C. under reduced pressure (2 Torr.) until nomore volatiles could be removed. The hydroxyl content of the product was6.43 meq/g. A degradable prepolymer was then made by first dewatering amixture of 770 g (0.77 mole) of CARBOWAX 1000, 45 g (0.5 mole) ofbutanediol, and 166.2 g (0.5 mole) of the lactated trimethylolpropaneprepared above for two hours at 100° C. and 1 Torr., then adding 600 g(3.45 mole) of toluene diisocyanate and maintaining the temperature at70° C. for one hour. The isocyanate content of the product was 2.68meq/g and the viscosity at 25° C. was 29,900 cp.

Sheets of foam were made by mixing 30 g of the prepolymer from Example 1with 30 g of a 2% (by weight) aqueous solution of Dow Corning siliconesurfactant DC-190 and pouring the foaming mixture between twopolyethylene sheets (9 inches wide). The sheets were then immediatelypulled between two cylindrical metal bars spaced 35 mils apart. Beforepouring the foaming polymer a single layer of environmentally degradablecotton cheesecloth was placed between the polyethylene films. After afew minutes, the polyurethane sheets had cured to foams, with thecheesecloth engulfed and secured near the center of the foam sheet. Thepolyethylene sheets were then removed. The foam sheets had expanded toapproximately 110 mils and had density of 0.12 g/cc (7.1 lb/cu.ft.).

A piece of the above-described sheet weighing approximately 0.1 g waskept in 100 ml of a 0.75% aqueous solution of Terg-A-Zyme® enzyme (fromAlconox, Inc., New York, N.Y.) at 80° C. until the foam disintegrated,leaving nothing but the cheesecloth. This required 4-5 days. Severalpieces of conventional urethane foam (produced by Armalay Sponge Co.,Walled Lake, Mich. and Vining Industries, Springfield, Ohio) did notdisintegrate after more than three weeks under the same conditions.

Examples 2-8

The following examples indicated in Table I below illustrate additionalexamples using CARBOWAX 1000, butanediol, lactated trimethylolpropane(TMP), as well as other polyols. The prepolymers disclosed below wereprepared under the same conditions as those described above inExample 1. These prepolymers were then used to prepare foams in a mannerdescribed in Example 1, except a cheesecloth was not used.

                                      TABLE I                                     __________________________________________________________________________    Starting Materials (Mole)                             Typical                 Example                                                                            CARBOWAX                                                                              PEG                                      Foam Density            Number                                                                             1000(a) 600(b)                                                                            Butanediol                                                                          Triol(c)                                                                           Lactated TMP(d)                                                                        TDI(e)                                                                            NCO(f)                                                                              Viscosity(g)                                                                         g/cc                    __________________________________________________________________________    2    1.00    --  --    --   0.382    3.83                                                                              2.46 (2.44)                                                                         15,000 0.07                    3    0.25    0.15                                                                              --    --   0.188    1.72                                                                              2.56 (2.41)                                                                         13,600 0.07                    4    0.25    --  0.25  --   0.188    1.72                                                                              3.29 (2.88)                                                                         16,400 0.06                    5     0.385  --  0.25  --   0.188    1.72                                                                              2.50 (2.88)                                                                         57,450 0.09                    6    0.77    --  0.45  --   0.376    3.44                                                                              2.76 (2.88)                                                                         11,000 0.09                    7    0.50    --  --    0.008                                                                              0.188    1.91                                                                              2.51 (2.58)                                                                          4,850 0.08                    8    1.00    --  --    0.016                                                                              0.376    3.56                                                                              2.29 (2.30)                                                                          4,680 0.08                    __________________________________________________________________________     (a)a polyoxyethylene glycol having a molecular weight of about 1000 from      Union Carbide.                                                                (b)a polyoxyethylene glycol having a molecular weight of about 600 from       Union Carbide.                                                                (c)random triol copolymer of 75% ethylene oxide and 25% propyleneoxide        having a molecular weight of about 7000.                                      (d)prepared as in Example 1.                                                  (e)toluene diisocyanate.                                                      (f)millequivalence of isocyanate functionality per gram of prepolymer.        (g)centipoise as measured at 25° C.                               

Example 9

A mixture of 225 g (2.5 moles) of 1,4-butanediol and 950 g (9 moles) of85% lactic acid was heated under reflux for 2.5 hours (106°-109° C.).Then, water and excess lactic acid were removed by distillation atatmospheric pressure as the temperature was raised gradually to 200° C.over a period of 11.5 hours. A total of 275 ml of volatile material wasremoved. The pressure was then reduced to 1-2 Torr. and the temperaturewas maintained at 132°-141° C. for an additional 4.5 hours, causingdistillation of a further 44 ml of volatile material. The non-volatileproduct weighed 853 g. The hydroxyl content of the product wasindicating that the butanediol lactate product was 66% pure.

A mixture of 500 g CARBOWAX 1000 (0.5 mole), 22.3 g (0.17 mole)trimethylolpropane, and 117 g the butanediol lactate prepared above wasdewatered two hours at 110° C. and 1-2 Torr. To this was added 431 g(2.47 moles) of tolylene diisocyanate and the temperature was maintainednear 70° C. for five hours. The isocyanate content of the product was2.60 meq/g and the viscosity was 16,700 cp at 25° C.

Example 10

The purpose of this example is to illustrate the reaction of apoly(oxyethylene) triol with lactic acid to form a lactated triol, andto illustrate the reaction of this triol with a diisocyanate; in thiscase, TDI. This differs from previous examples of lactated prepolymersin that the previous examples used a high molecular weight diol and alow molecular weight triol. In this example, the triol had a nominalmolecular weight of 990.

Reaction with Lactic Acid

A mixture of TPEG 990 (300 g, 0.303 mole), an ethylene oxide-based triolwith nominal molecular weight of 990 from Union Carbide, and 196.2 g(1.85 moles) of 85% lactic acid was heated to 200° C. over a period of13 hours in order to form the lactate ester. During this time, 44 g ofwater was distilled from the mixture. The product was dewatered for anadditional four hours at 160°-198° C. and 1-2 Torr., causing removal ofan additional 12 g of volatile materials. The dried lactate product wasfound to have a water content of less than 0.1%.

A mixture of 300 g of the lactate product and 142.8 g (0.82 mole) ofOLIN TYPE 2® TDI from The Olin Corp., Stamford, Conn.) was heated at 70°C. for eight hours. During the last two hours, the isocyanate content ofthe reaction product remained constant at 2.15 meq./g. The product, orprepolymer, had viscosity at 25° C. of 35,000 cp.

A sheet was made essentially as described in Example 1 using 50 g of theprepolymer and 50 g of water. When dried, the sheet had a density of0.15 g/cc and water capacity of 9 grams per gram. It disintegrated in aboiling phosphate buffer solution in 110 minutes.

Example 1 "Fully Lactated" Prepolymer

A mixture of 1540 g (1.54 moles) of CARBOWAX® 1000, 103.2 g (0.77 mole)of trimethylolpropane, and 1030 g (9.27 moles) of 85% lactic acid washeated to 200° C. during two hours, causing the distillation of 234 g ofwater. The temperature was maintained at 200° C. for an additional 41/2hours. The total amount of water removed was 260 g. Following this,unreacted lactic acid and other volatile materials were removed underreduced pressure at 200° C. and approximately 1 Torr. until distillationstopped. This required two hours and the total amount of distillate was194 g. The lactated polyol product that remained undistilled weighed2227 g. A determination of hydroxyl content indicated a value of 2.3meq/g.

To 700 g of the lactated polyol product was added 307 g of TDI. Thismixture was allowed to react at 70° C. for seven hours, after which timethe isocyanate content was found to be 1.82 meq/g and the viscosity atambient temperature was 92,000 cp.

A sheet, 0.1 inch thick, was made from equal weights of theisocyanate-capped prepolymer and water as described in Example 1. Piecesof this sheet were found to fragment into fine powder after 3-4 hours ina 2% aqueous solution of dibasic sodium phosphate at 90°-100° C.

Example 12 Example of Prepolymer Composed Only of Lactated Diols andDiisocyanate, with Strength Obtained Through Allophanate Formation

A mixture of 770 g (0.77 mol) of CARBOWAX® 1000, 40.9 g (0.385 mole) ofdiethylene glycol, and 515 g (4.86 moles) of 85% lactic acid was heatedto 200° C. and maintained at this temperature for an additional halfhour, causing removal of 122 g of water. The unreacted lactic acid andother volatiles were removed by distillation at approximately 1 Torr. at200° C. The water content of the product lactated diols thus was reducedto less than 0.05% by weight. To 700 g of the lactated polyols was added301.1 g of TDI and the resulting mixture was allowed to react for fourhours at 70° C. The resulting isocyanate-capped prepolymer had viscosityof 90,500 cp and isocyanate content of 1.51 meq/g. It was formed into asheet, using equal weights of prepolymer and water, according to theprocedure described in Example 1. Pieces of this sheet, in a 2% aqueoussolution of dibasic sodium phosphate at 90°-100° C., were reduced tofine powder in one hour.

Example 13 Synthesis of Prepolymer Using a Mixture of Acids

A mixture of 350.7 g (2.4 moles) of adipic acid, 63.3 g (0.6 mole) of85% lactic acid, 254.7 g (2.4 moles) of diethylene glycol, and 26.8 g(0.2 mole) of trimethylolpropane was heated at atmospheric pressure foreight hours as the temperature was raised gradually to 233° C. until nomore water was evolved. The hydroxyl content of the polyester triolproduct was 1.24 meq/g, indicating an equivalent weight of 806.

Preparation of Foam Sheet

Forty-six grams of the polyester triol product was mixed with 1.5 g ofwater, 0.7 g of stannous octoate, and 0.9 g of Union Carbide siliconesurfactant L-520®. To this mixture was added 10.9 g of TDI. The mixturewas stirred vigorously for 70 seconds and the resulting froth was pouredbetween two polyethylene films with dimensions of approximately 9 inchesby 13 inches, and the assembly was passed between two cylindrical barsspaced 1/16 inch apart in order to spread the froth into a sheet ofuniform thickness. After two hours, the polyethylene film was strippedfrom the polyurethane sheet, which was found to be fine-celled and tohave a density of 0.24 g/cc.

Preparation of Laminated Bait

Twenty-three grams of the polyester triol was mixed with 15 g of apowdered fish attractant, 0.75 g of water, 0.35 g of stannous octoate,and 0.45 g of silicone L-520. One-half of this paste (12.3 g) wasstirred quickly with 2.73 g of TDI, and 2.1 g of this reacting adhesivecomposition was used to adhere two strips of the polyurethane sheetwhich weighed 2.37 g each. The following day the laminate was found toweigh 6.98 g, indicating that it contained 15% by weight of the solidattractant powder. A second laminated strip made in a similar way wasfound to contain 21% by weight of the attractant.

Extraction of Bait Composition

A three-gram portion of the laminate having 21% by weight of solidattractant encapsulated in the central laminating adhesive was shaken atmoderate speed on a rotary shaker for one week at 18° C. with 400 ml ofwater. Samples were removed periodically for analysis of phosphorous, acomponent of the attractant mixture, as a means of estimating the amountof attractant that had been extracted. After two hours, 25% as muchphosphorous had been extracted as was extracted during the entire week.After 24 hours, 73% of the extractable phosphorous had been removed, onthe same basis. The total amount of phosphorous extracted in one weekwas nearly the amount calculated to have been present, indicating thatnearly all of the attractant had been extracted. Furthermore, theextracted bait sheet, after drying, had lost 18% of its weight but hadnot changed significantly in appearance.

Degradability of the Bait

A piece of the foamed polyurethane sheet weighing 1.25 g, was placedinto a stirred solution of 4.7 g of Na₂ HPO₄ in 250 ml of water (pH 9.1)which was kept at 95°-100° C. The sheet disintegrated into a very finewhite powder within 15 minutes. A similar piece of the laminated productof Example 10 was tested in the same way. It delaminated in six minutes,broke into many large scraps within 10-15 minutes, and formed finepowder within 110 minutes. The longer survival time appeared to be dueto the dense adhesive layer which resisted hydrolysis to a greaterdegree than the foam.

Example 14 Non-foamed Articles Synthesis of Elastomer

The following examples in Table II below illustrate non-foamedpolyurethane elastomers or gels made according to the inventiondescribed herein. The degradable prepolymer of Example 1 was reactedwith varying proportions of a trifunctional polyethylene glycol ofnominal molecular weight 990 ("TPEG 990") and polyethylene glycol ofnominal molecular weight 400 ("PEG" 400) (both available from UnionCarbide). The mixture was degassed under vacuum and poured into 3/8"inner diameter vinyl tubing, and allowed to cure at about 100° C. fortwo hours.

                  TABLE II                                                        ______________________________________                                        Composition of Various Elastomers                                                  Degradable                                                               Run  Prepolymer                                                                              TPEG 990       PEG 400                                         ______________________________________                                        a    7.0 g (17.6                                                                              5.8 g (17.6 meq OH)                                                                         0                                                    meq NCO)                                                                 b    7.0 g (17.6                                                                              4.6 g (14.1 meq OH)                                                                         0.70 g (3.5 meq OH)                                  meq NCO)                                                                 c    7.0 g (17.6                                                                             3.48 g (10.5 meq OH)                                                                         1.41.g (7.1 meq OH)                                  meq NCO)                                                                 d    7.0 g (17.6                                                                             2.32 g (7.0 meq OH)                                                                           2.1 g (10.6 meq OH)                                 meq NCO)                                                                 e    7.0 g (17.6                                                                             1.16 g (3.5 meq OH)                                                                          2.81 g (14.1 meq OH)                                 meq NCO)                                                                 f    7.0 g (17.6                                                                             0.58 g (1.8 meq OH)                                                                          3.16 g (15.8 meq OH)                                 meq NCO)                                                                 ______________________________________                                    

The elastomers were found to be increasingly soft as the amount oftrifunctional material (TPEG 990) was reduced.

The elastomers were also prepared from using glycerol as thecrosslinking agent. The formulations using glycerol (from J. T. Baker,Phillipsburgh, Pa.) contained PEG 400 and a curing catalyst, DABCO®triethylene diamine (from Air Products, Allentown, Pa). The addition ofDABCO® catalyst allowed the polymer to be cured at room temperature.

The following proportions (Table III) were used to make the elastomerscontaining glycerol.

                  TABLE III                                                       ______________________________________                                             Degradable                                                               Run  Prepolymer                                                                              Glycerol        PEG 400                                                                              DABCO                                   ______________________________________                                        a    7.0 g (17.6                                                                              0.054 g (1.76 meq OH)                                                                        3.16 g 0.01 g                                       meq NCO)                                                                 b    7.0 g (17.6                                                                             0.1078 g (3.52 meq OH)                                                                        2.81 g 0.01 g                                       meq NCO)                                                                 c    7.0 g (17.6                                                                             0.1616 g (5.28 meq OH)                                                                        2.46 g 0.01 g                                       meq NCO)                                                                 d    7.0 g (17.6                                                                             0.2155 g (7.04 meq OH)                                                                        2.11 g 0.01 g                                       meq NCO)                                                                 e    7.0 g (17.6                                                                             0.2694 g (8.8 meq OH)                                                                         1.76 g 0.01 g                                       meq NCO)                                                                 ______________________________________                                    

The elastomers were increasingly stiff as the level of glycerolincreased. At 10% glycerol, the material was slightly tacky, but eventhis material was stronger than the typical plasticized poly(vinylchloride) bait "worms." This latter elastomer lost its physicalintegrity on soaking in deionized water for five days without stirring.It liquified and settled to the bottom of the container.

Preparation of Attractant Loaded Gels

A fish-attractant mixture (0.6 g) was dissolved in 20 g of deionizedwater. To this solution 4.0 g of gel prepolymer, was added and mixed for45 seconds. The liquid reaction mixture was then poured into an aluminumfoil mold containing cheesecloth and allowed to gel. The gels could alsobe prepared without cheesecloth, which is used to provide strength. Thefollowing samples were tested.

                  TABLE IV                                                        ______________________________________                                        Compositions of Various Gels Containing Attractants                           Run   Prepolymer Attractant water  % Prepolymer                               ______________________________________                                        a     2.0 g      0.30 g     20.0 g 10                                         b     3.0 g      0.45 g     20.0 g 15                                         c     4.0 g      0.60 g     20.0 g 20                                         ______________________________________                                    

Release Rates

Samples were assayed for attractant release by placing them in ameasured amount of deionized water (400 g) and gently agitating on anorbital shaker at 18° C. Aliquots of water were taken out at specifictime intervals and release was calculated by monitoring the phosphorousconcentration resulting from release of attractants. FIG. 2 shows therelease of attractants (based on phosphorous analysis) of containingvarious attractants. As the prepolymer concentration decreases in a gel,the crosslinked density also decreases. The release rate of attractantincreases as the crosslink density decreases.

DEGRADABILITY OF FOAMS Example 15

Three methods were used to compare the degradation rate of the variousfoams.

a. 100 mg of the foam was kept in 100 ml of a 0.75% aqueous solution ofTerg-A-Zyme enzyme (from Alconox, Inc.) at 80° C. until the foamdisintegrated into small particles. A foam prepared according to themethod in Example 1 completely disintegrated leaving the cheesecloth.This required 4-5 days. Several pieces of conventional urethane foam(produced by Armalay Co. or Vining Industries) did not disintegrateafter more than three weeks under the same conditions.

b. In this method three foams were made by mixing 40 g of the prepolymerfrom Example 9 with 40 ml of 3 different 2% aqueous solution ofsurfactants. The three surfactants used were BASF's Pluronic L-62 andPluronic F-68 surfactants, and Dow-Corning's DC-190 surfactant. Theresulting three foams possessed medium sized, coarse, and fine cells,respectively, and all three were flexible. The foams were individuallystirred in a 2% basic sodium phosphate solution (pH 9.1) at 90°-100° C.until the foam disintegrated through a combination of hydrolytic andmechanical action. The coarse-celled foam made with F-68 surfactantsurvived 32 minutes; the medium-celled foam made with L-62 surfactantsurvived for 145 minutes, and the fine-celled foam made with DC-190surfactant survived for 130 minutes.

The foam of Example 10 disintegrated in 110 minutes. Pieces of the foamfrom Example 11 were found to fragment into fine powder after 3-4 hours.

The foamed polyurethane sheet of Example 13 disintegrated into a veryfine white powder within 15 minutes; a similar piece of the laminatedbait delaminated in six minutes, broke into many large scraps within 10to 15 minutes, and formed fine white powder within 110 minutes.

By contrast, a nondegradable foam made in a similar manner from W. R.Grace & Co.-Conn.'s HYPOL® 2000 polyurethane prepolymer and a 2% aqueoussolution of PLURONIC® L-62 surfactant survived in the same test for23-24 hours.

c. In this method the hydrolytic degradation of various foams wascarried out in a pH of ocean water) weak buffer (10 mm phosphate buffer)at 90° C. 750 mg of the foam was suspended in 200 ml of the buffer at90° C. A very gentle rotational stirring was introduced so as not tocause a mechanical degradation. This may be considered as an acceleratedtest for hydrolytic degradation in the marine water (except thatmicrobes were absent). The time required for the foams to fall apartinto small particles were compared. After disintegration, the particlessettled to the bottom of the solution. The degradable foam of Example 9(using DC-190 surfactant) fell apart into small particles in 3-4 hours.Commercial polyurethane foams like Scottfoam® (900Z) (KnollInternational Holdings, Inc. Addystone, Pa.) and General Foam®(6400L773) (from General Foam, West Parsippany, N.J.) degraded in 22days and 13 days, respectively. Both of the commercial foams arepolyester urethanes derived from adipic acid, diethylene glycol and TDI.

Sustained Release Rates Example 16

A mixture of powdered synthetic sensory additives was comminuted in amortar and pestle. A three gram sample of this powder was dissolved in100 ml of water, which was then soaked into an approximately 1/8 inchsheet of the foam illustrated in Example 1. The sample piece of foamweighed 16.9 g. The sheet was immersed until it contained 15% by weightof attractants and then dried. Seven pieces of this sheet productweighing a total of 1.4 g each were stirred with 100-ml portions ofwater at moderate speed with a magnetic stirring bar. The water wasfiltered and evaporated to recover the attractants. After 10, 30 and 120minutes, the samples had released 71%, 82% and 90%, respectively, byweight of the total amount that was recovered at the end of theexperiment by squeezing the foam.

In an experiment similar to the one above, a phosphorus-containingcompound was added to the additive mixture to provide phosphorous foranalysis by inductively-coupled plasma elemental analysis (ICP)instrument Model 3410, (from Fissons-ARL, Valencia, Calif.). Sampleswere shaken in a jar to measure the rate of release. After 30 and 120minutes, the foam had released about 57% and 79% of the availablephosphorous. The foam had released nearly all of its load between 4 and6 hours. When small pieces of the additive-containing foam were put intoan aquarium with pinfish or with sea bass, they were readily consumed bythe fish.

Encapsulation of Solid Chemosensory Attractants Example 17

The prepolymer of Example 1 was diluted to 80% concentration (W/W) bymixing 27.6 g of the prepolymer with 6.9 g of methyl ethyl ketone. To7.7 g of the 80% solution was added 1.93 g of a phosphorous-containingchemoattractant solid mixture similar to Example 16. A paste of themixture was then made by mixing. Then 1.2 g of this paste was applied onthe degradable urethane foam sheet of Example 3 having approximately0.31 cm thickness and 0.6 g weight. A second sheet of the same foam of asimilar dimension and weight was placed on the paste and the two sheetsstuck together overnight on the bench top so that moisture (humidity)curing took place while the solid chemosensory attractants were therebyencapsulated in the center of the laminate. Other baits were prepared ina similar manner. Table V describes various configurations of baits.

                  TABLE V                                                         ______________________________________                                        CONFIGURATION OF VARIOUS ARTIFICIAL BAITS                                     Bait      Foam Thickness                                                                            Weight Ratio Other                                      Number    (Mils)      Foam/Paste   Additives                                  ______________________________________                                        1          75         1:1          None                                       2         150         1:1          None                                       3         150         1:1          Polyox ®                               4         150         2:1          None                                       ______________________________________                                         Endnotes:                                                                     (a) Bait thickness is approximately twice the thickness of the foam.          (b) Paste contains 20% by weight chemosensory attractants and 64% by          weight degradable prepolymer and 16% methyl ethyl ketone.                

Additional Sustained Release Rates Example 18

Four bait samples prepared according to Example 17 were introduced intoa bottle containing 400 ml deionized water. The baits were prepared in asandwich-type structure similar to the bait described in Example 13. Thebottle was then gently agitated on an orbital shaker at 18°±1° C.Aliquots of water (5 ml) were taken at different intervals and assayedfor phosphorous using inductively coupled plasma (ICP). FIG. 3illustrates the release profile of phosphorous from various samplesreported in Table V.

What is claimed is:
 1. A degradable bait for aquatic or marine organisms wherein the bait comprises(a) a first layer of a degradable polyurethane polymer wherein the polymer has hydrolytically labile ester linkages formed from reaction of a polyol with an α-hydroxy carboxylic acid; (b) a second layer of a degradable polyurethane polymer wherein the polymer has hydrolytically labile ester linkages formed from reaction of a polyol with an α-hydroxy carboxylic acid; (c) an adhesive layer between said first and second layers of degradable polyurethane polymer, said adhesive layer comprising sensory stimulant additives in an amount effective for release from the bait in an aqueous medium at a sustained rate sufficient to attract aquatic or marine organisms.
 2. A degradable bait according to claim 1 wherein the layers are adhered together by a degradable adhesive.
 3. A degradable bait according to claim 2 wherein the adhesive is a polyurethane polymer which has hydrolytically labile ester linkages.
 4. A degradable bait according to claim 2 wherein the polyurethane polymer and the polymer adhesive comprise the same polymer.
 5. A degradable bait according to claim 4 wherein the polyurethane polymer foam and the polymer adhesive are prepared from a prepolymer which is the reaction product of(a) a condensation product from one or more polyols selected from the group comprising(i) monomeric low molecular weight aliphatic alcohols having from 2 to 8 hydroxyl groups per molecule; and (ii) essentially linear polyether or polyester polymeric polyols; and an alpha hydroxy carboxylic acid, and (b) a polyisocyanate.
 6. A degradable bait according to claim 5 wherein the condensation product is the reaction product of trimethylolpropane and lactic acid.
 7. A degradable bait according to claim 1 wherein the bait in addition comprises a reinforcing layer.
 8. A degradable bait according to claim 7 wherein the polyurethane polymer layers and the reinforcing layer are laminated together such that at least one reinforcing layer is between the polymer layers.
 9. A method of attracting aquatic or marine organisms comprising placing in the vicinity of said aquatic or marine organisms a degradable bait comprising(a) a first layer of a degradable polyurethane polymer wherein the polymer has hydrolytically labile ester linkages formed from reaction of a polyol with an α-hydroxy carboxylic acid; (b) a second layer of a degradable polyurethane polymer wherein the polymer has hydrolytically labile ester linkages formed from reaction of a polyol with an α-hydroxy carboxylic acid; (c) an adhesive layer between said first and second layers of degradable polyurethane polymer, said adhesive layer comprising sensory stimulant additives in an amount effective for release from the bait in an aqueous medium at a sustained rate sufficient to attract aquatic or marine organisms.
 10. A method according to claim 9 wherein the bait comprises a degradable adhesive.
 11. A method according to claim 10 wherein the adhesive is a polyurethane polymer which has hydrolytically labile ester linkages.
 12. A method according to claim 10 wherein the degradable polymer and the adhesive comprise the same polymer.
 13. A method according to claim 12 wherein the degradable polymer and the polymer adhesive are prepared from a prepolymer which is the reaction product of(a) a condensation product from one or more polyols selected from the group comprising(i) monomeric low molecular weight aliphatic alcohols having from 2 to 8 hydroxyl groups per molecule; (ii) essentially linear polyether or polyester polymeric polyols; and an alpha hydroxy carboxylic acid, and (b) a polyisocyanate.
 14. A method according to claim 13 wherein the condensation product is the reaction product of trimethylolpropane and lactic acid.
 15. A method according to claim 9 wherein the bait in addition comprises a reinforcing layer.
 16. A method according to claim 15 wherein the degradable polymer layers and the reinforcing layer are laminated together such that at least one reinforcing layer is between the polymer layers. 